Infill and Oversail Systems

In multi-storey framed construction light steel external walling systems are used extensively to create a rapid dry building envelope on a range of building types and are an economic and efficient method of providing facade walls. There are two common types of walling systems – infill and oversail walls, also known as continuous walling. 

Infill Walling is a term for external walls that are built between the floors of the primary structural frame of a building which provide support for the cladding system. Much lighter and thinner than conventional block work, light steel infill walls do not apply heavy line loads to floors. 

Infill walls do not support floor loads, but they resist wind loads applied to the facade. Light steel infill walls using vertical C section studs are prevalent within both steel and concrete-framed buildings and have largely replaced masonry or timber alternatives. 

The C section size and spacing selected depend on the structural requirements. The spacing is also selected to be compatible with the external facade materials. With layouts engineered to support windows and openings and additional studs around openings for lateral tie back for brick tie channels and brackets for facades. The panels which fit between the elements of the primary structural frame consist of a bottom track attached to the floor and a head track attached to the underside of the floor above and allowing for building deflection. Wall panels can be prefabricated as storey-high units offsite or site assembled from C sections that are delivered cut-to-length. So reducing noise and risk on-site as no cutting is required. 

Light steel infill walling systems can be used with a range of cladding types including 'heavy' cladding, such as brickwork, or 'lightweight' claddings such as insulated renders and rain-screens.

• Light weight, speed and ease of installation are important constructional advantages 
• Rapid installation permits much earlier access for follow-on trades 
• Installation process is 'dry' so shrinkage and other drying-out problems are eliminated 
• Large windows, parapets and other architectural features can be incorporated 
• 120 minutes fire resistance can be achieved with certain boarding systems 
• Can achieve excellent acoustic performance when combined with facade elements 
• High levels of thermal performance can be achieved with proprietary insulation, as per system data 
• Complete infill panel systems are now available which have been tested from inside room to cavity and cavity to inside which offer system warranties and 'golden thread' assurance removing risk for client, developer, main contractor and insurer 

Oversail Walling Systems

As an economic and efficient method of providing external walling systems for steel and concrete framed buildings, light steel external oversail walls are designed to resist wind loading on facades and to support their own weight and that of attached lightweight cladding materials. 

Typically constructed from the outside of the building, continuous walling 'oversails' the edge of the primary structure with studs being fixed via cleats maximising floor area. The components used in oversail are similar to those used for infill walling. However, there are some significant differences that must be considered in design and construction. 

Oversail walls are placed externally to the primary structural frame rather than between the floors as in the case of infill walls. Oversail walling systems are particularly suited to situations where cladding materials are sensitive to differing movement of the main frame. Adequate base support must be provided to accommodate vertical loading from the cladding. Openings in the building facade and a variety of cladding options can be accommodated. The continuous external walling system consists of vertical light steel C sections and bracket connections to fix them to the primary frame. Allowance for movement of the primary frame must be incorporated into the connections, usually by use of slotted connections. 

Dead weight of masonry cladding must be supported directly by the primary structure or foundations. However, light steel external walling systems can generally provide horizontal support against wind through the inclusion of a proprietary system of brick tie channels and brick ties positively fixed back to the stud. 

In addition to structural requirements, the design of both infill and oversail external walling systems must also consider fire resistance, condensation risk, weathertightness, thermal insulation and acoustic performance, and must allow for interfaces at windows, patio doors and balconies.

USEFUL DOCUMENTS

SCI Publications including:

P402 - LSF Residential Guide

P302 - LSF Modular Residential

P262 - Durability of Light Steel Framing in Residential Building 

P272 - Modular Architects Guide 

P348 - Building Design using Modules

P367 - Energy efficient Housing using Light Steel Framing 

P370 - Sustainability of steel in housing 

P407 - BIM and 3D Modelling in Light Steel Construction

P424 - Fire resistance of light steel framing

P426 - Uninterrupted Height of Masonry Cladding to Light Steel Framing

SCI Technical Information Sheets including:

ED014 - Light Steel Module construction

ED015 - Acoustic Performance

ED016 - Fire Performance

ED017 - Design and Installation of Light Steel External Wall Systems

ED019 - Thermal Performance

ED020 - Sustainability of light steel construction

ED021 - Robustness

ED022 - Durability

>>Download the full LSFA Specification and Engineering Guide via our Library

Image credit: Ayrshire Metals